Structural pre-conceptual design studies for an EU DEMO equatorial EC port plug and its port integration

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Highlights

  • A first pre-conceptual design concept for an DEMO EC launcher is presented.

  • It includes all relevant components on a pre-conceptual basis.

  • General design requirements are taken into account.

Abstract

For the EU DEMO Tokamak, Electron Cyclotron (EC) launching systems for plasma heating and stabilization are under development. Various concepts for the optical system are currently studied of which the Mid Steering Antenna (MSA) with a steering mirror at a recessed position behind the breeding blanket (BB), the Open Ended Waveguide (OEWG) concept with quasi-optical beam propagation by fixed mirrors only and the Remote Steering Antenna (RSA), currently seen as back-up solution, are the basic ones. In addition, hybrid solutions, which means a port plug with different launcher concepts, are taken into consideration. In parallel, design drafts for a generic equatorial port plug are sketched with the aim to provide a versatile structural system, which allows customized installation of the potential optical systems. This paper presents a pre-conceptual hybrid design of an equatorial EU DEMO EC port plug based on MSA for plasma stabilization and OEWG for plasma heating, taking into account the exact port position with respect to the toroidal field coil, mechanical integrity, heat dissipation, neutronic shielding requirements, design integration and maintenance concepts.

Introduction

For the EU DEMO Tokamak, EC launching systems for plasma heating and stabilization are under development. Based on the 2017 engineering baseline, the 2018 physics baseline, and the port plugs being radially recessed to the level of the Vacuum Vessel (VV) inner shell and hence not blocking the vertical extraction of the outboard BB segments [1], a pre-conceptual design study of an EU DEMO equatorial EC launcher has been made. For optimum performance [2], the design study features a hybrid concept with MSA and also OEWG antennas. The MSA is considered for plasma stabilization and has a (partially) quasi-optical beam layout with steerable mirrors at a recessed position behind the radial extension of the breeding blankets [3]. Beside the MSA, also an OEWG antenna is designed for the EC Launcher, which will be used for plasma heating only.

The pre-conceptual design of the EC Launcher features structural components, which can accommodate this hybrid millimeter-wave system accordingly. It also comprises shielding elements, cooling installations and interface provisions for the integration of the optical system. All structural components were designed with respect to available design requirements on position and dimensions, mechanical and thermal loads, nuclear constraints, physics performance, maintenance and geometrical and functional interfaces.

The CAD model is set up by parametric skeleton geometries, which guarantees a relatively flexible design to cope with moving targets and potential future baseline changes (e.g. the concept of an RSA).

Section snippets

DEMO Engineering baseline 2017

Fig. 1 outlines a cross-section of the EU DEMO engineering baseline model 2017 [4], having installed the EC launcher already. This model provides the current layout of the EU DEMO Tokamak, including the breeding blankets, the vacuum vessel with its vertical upper ports, the bioshield, the cryostat and many more interfacing and design-relevant components of an EC Launcher for a future EU DEMO reactor.

EC Launcher design

Beside the engineering baseline model 2017, the EC launcher design is made according to the physics baseline model 2018 and the latest optical system design, provided by the Italian Institute for Plasma Science and Technology (ISTP) [2], (cf. Fig. 2).

It is comprised of an MSA with two sections of three beamlines each for NTM (Neo-classical Tearing Modes) control and two further OEWG antenna sections with eight waveguides each for plasma heating. Both systems are arranged in a symmetric layout

Equatorial port for the EC launcher

The equatorial ports in the current EU DEMO concept offer the possibility of customized dimensions for particular installations. The dimensional limits are set on principle by the poloidal clearance between the poloidal field coils and the toroidal clearance between the toroidal field coils only while the maximum radial extension is defined by the position of the Bioshield.

This means in fact a maximum height of the equatorial port of 4000 mm and a maximum width of around 4700 mm. The greatest

EC Launcher port plug design

The mirrors of the In-Vessel millimeter wave system require precise and safe installation into the DEMO equatorial port. Thus they are mounted into dedicated port plugs, which are basically massive structural components with customized shapes and cut-outs which guarantee undisturbed beam propagation into the plasma, maximum neutron shielding properties and straightforward maintenance processes. Due to their position close to the plasma also active cooling of the plugs will be required.

One

Maintenance concept

Preliminary evaluations indicate the installations of the EC launcher as to be maintained either regularly or on purpose during EU DEMO operational lifetime. In order to perform the required procedures in an effective way, the replacement of the plugs is preferred instead of the replacement (or repair) of individual mirrors or other smaller sized components.

The SM EPP and its integration is designed for multiple replacement during DEMO operation, which is why the whole procedure is planned to

Closure plate assembly

The maintenance concept described in chapter 6 requires an adequate layout for the accessible vacuum boundary of the equatorial port. Thus, this so-called closure plate has been sub-divided into a staggered assembly, consisting of several elements, to be opened for dedicated purpose.

The main closure plate (1) is formed as a massive plate, which areal dimension is 3880 × 2830 mm². It has a thickness of 110 mm and carries all other sub-plates. It is attached to the port extension by bolts and its

Neutronic considerations

In the EU DEMO plant description document [6], neutronic design limits are given regarding neutron damage, Helium production and Shutdown dose rates for several areas and types of components for an EU DEMO reactor.

Since the demonstration of fulfilling these design limits with the pre-conceptual design can be made not before a dedicated MCNP neutronic analysis has been run, a rather conservative approach has been chosen for designing the EC Launcher components. Typical consequences from this

Versatility of the design

The present pre-conceptual design of the EC launcher prefers a combination of OEWG with a quasi-optical dogleg beam configuration for plasma heating and a MSA concept for NTM stabilization. However, the current concept of an equatorial port with dedicated port plugs for individual millimeter-wave component assemblies and optional auxiliary shield blocks has the freedom to be adapted easily for further millimeter wave concepts as well. Another important feature, which offers particular design

Conclusion

A EUROfusion task has been placed to advance the pre-conceptual design for an EU DEMO EC launcher. Starting from the engineering baseline 2017 model, the physics baseline 2018 and a new MSA and OEWG antenna design from ISTP, a design concept has been established and corresponding CAD models were created. Beside proper integration into the baseline models, also RH maintenance schemes and neutronic aspects were taken into account. The model will be the basis for forth-coming MCNP- and EM-analyses.

CRediT authorship contribution statement

Peter Spaeh: Conceptualization, Methodology, Software, Data curation, Writing - original draft, Vizualisation. Christian Bachmann: Conceptualization, Project administration, Funding acquisition. René Chavan: Investigation. Aljaz Cufar: Software, Formal analysis, Data curation. Thomas Franke: Conceptualization, Methodology, Writing - review & editing, Project administration. Dirk Strauss: Conceptualization, Supervision, Project administration, Funding acquisition. Minh Quang Tran: Supervision,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the EURATOM research and training programme 2014-2018 and 2019-2020 under grant agreement No. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

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